Psychrometry: is the study of moist air. Before starting study of refrigeration process everyone should take a basic knowledge of Psychrometry. It is consist of these topics, i . DBT (Dry Bulb temperature) ii. WBT (Wet Bulb temperature) iii. DPT (Dew Point temperature) iv. Specific Humidity v. Relative Humidity vi. Degree of Saturation DBT: Dry bulb temperature is the normal temperature of the air in room. When a thermometer gives normal temperature in atmospheric or ambient, that is called DBT. WBT: Wet Bulb Temperature is different from DBT. From it's name we get something different. If Wet something like a Wet clothes is wrapped in the sensing side of the thermometer than which reading it will give, that is known is WBT. The wet clothes moisture will consume by normal air or atmospheric air. Air is always ready to consume moisture if it's Relative Humidity ( RH) is less than 100%. Relative Humidity is the term, what represent the amount of moisture are in the